# Clinical Cases: Aerospace Medicine

## Case 1: Spatial Disorientation and G-LOC in Fighter Pilot

### Patient Presentation
**Demographics:** 29-year-old male active-duty fighter pilot (F-16C)

**Chief Complaint:** "I blacked out during a high-G turn and nearly lost the aircraft."

**History of Present Illness:**
Captain R.M. was performing a 7.5G sustained turn during an air combat maneuvering training sortie when he experienced progressive peripheral vision loss (greyout) followed by complete loss of consciousness (G-LOC). The Anti-G Straining Maneuver (AGSM) was reportedly initiated but may have been performed incorrectly. Onboard flight recording confirmed 12 seconds of incapacitation with the aircraft descending 3,200 feet before recovery.

Upon regaining consciousness, the pilot reported initial confusion, dreamlike mentation, and difficulty recalling procedures for approximately 15 seconds (relative incapacitation period). He was able to recover the aircraft and return to base uneventfully. He denied any prodromal symptoms prior to the event other than the expected visual changes. No prior episodes of G-LOC in 6 years of fighter operations.

Post-flight evaluation revealed the pilot had slept only 4 hours the preceding night due to mission planning, had consumed minimal fluids that day, and had not eaten breakfast. His anti-G suit was found to have a slow leak in the left calf bladder, reducing its protective capability by an estimated 0.5-1.0G.

**Past Medical History:**
- No significant medical history
- Annual flight physicals consistently within standards
- Centrifuge training completed 18 months prior with G-tolerance to 9.0G

**Medications:**
- None
- Denied use of supplements or performance-enhancing substances

**Social History:**
- Non-smoker, occasional social alcohol (none within 12 hours of flight per regulation)
- Regular physical exercise program including weight training and running
- Recently increased operational tempo with 3 sorties in the past 48 hours

**Family History:**
- Father with hypertension (age 58)
- No family history of cardiac arrhythmia or sudden cardiac death

### Physical Examination
- **Vital Signs:** BP 118/72 mmHg, HR 78 bpm, RR 14, SpO2 99% on room air, Temp 36.8°C
- **General:** Alert, oriented, well-developed male in no acute distress
- **HEENT:** Pupils equal and reactive, no retinal hemorrhages on fundoscopy, TMs intact bilaterally
- **Cardiovascular:** Regular rate and rhythm, no murmurs, normal S1/S2
- **Neurological:** Cranial nerves II-XII intact, motor strength 5/5 all extremities, coordination normal, Romberg negative
- **Musculoskeletal:** Petechiae noted on bilateral lower extremities consistent with G-exposure; no edema

### Workup and Results

**Laboratory Studies:**
| Test | Result | Reference Range |
|------|--------|-----------------|
| Hemoglobin | 15.2 g/dL | 13.5-17.5 g/dL |
| Hematocrit | 44% | 38.3-48.6% |
| Sodium | 139 mEq/L | 136-145 mEq/L |
| Potassium | 4.1 mEq/L | 3.5-5.0 mEq/L |
| Glucose (fasting) | 72 mg/dL | 70-100 mg/dL |
| Troponin I | <0.01 ng/mL | <0.04 ng/mL |
| TSH | 2.1 mIU/L | 0.4-4.0 mIU/L |

**Imaging/Additional Studies:**
- **ECG:** Normal sinus rhythm, normal axis, no ST changes, QTc 410 ms
- **Echocardiogram:** Normal LV function, EF 62%, no structural abnormalities
- **MRI Brain:** No acute intracranial pathology, no evidence of ischemic injury
- **Tilt table test:** Normal hemodynamic response
- **Centrifuge re-evaluation:** Adequate AGSM technique restored after retraining; G-tolerance 8.5G with functional anti-G equipment

### Clinical Image

![Physiological mechanisms of G-induced loss of consciousness](case_01_image.jpg)

*Diagram illustrating the cardiovascular physiology of G-LOC, showing hydrostatic pressure effects on cerebral perfusion during sustained positive Gz acceleration. Source: Educational illustration.*

### Diagnosis
**G-Induced Loss of Consciousness (G-LOC) — Multifactorial**

**Key Diagnostic Criteria:**
- Witnessed loss of consciousness during sustained high-G maneuvering
- Classic greyout-to-blackout progression consistent with retinal and cerebral hypoperfusion
- Contributing factors identified: fatigue, dehydration, hypoglycemia, defective anti-G equipment
- No underlying cardiac or neurological pathology on comprehensive workup

### Treatment Plan
1. Temporary grounding (DNIF — Duties Not Including Flying) for 72 hours minimum
2. Anti-G suit inspection and replacement of defective equipment
3. Mandatory AGSM retraining with centrifuge proficiency demonstration
4. Crew rest compliance counseling — minimum 8 hours sleep before sorties
5. Hydration and nutrition protocol education (minimum 2L fluid, adequate caloric intake pre-flight)
6. Return to flying status after flight surgeon clearance and demonstrated centrifuge proficiency
7. Aeromedical review of squadron operational tempo

### Key Learning Points
- G-LOC occurs when cerebral perfusion pressure drops below the critical closing pressure of cerebral vasculature, typically at sustained loads above 4-5 Gz without protective measures
- The relative incapacitation period following G-LOC recovery (confusion, disorientation) averages 12-24 seconds and represents the most dangerous phase for aircraft recovery
- Fatigue, dehydration, and hypoglycemia significantly reduce G-tolerance by 0.5-1.5G
- The Anti-G Straining Maneuver (AGSM) combining the L-1/M-1 technique with anti-G suit inflation can increase G-tolerance by 3-4G
- A systematic aeromedical approach must rule out underlying cardiac or neurological pathology before attributing LOC solely to G-forces

---

## Case 2: Decompression Sickness in Astronaut

### Patient Presentation
**Demographics:** 42-year-old female astronaut and mission specialist (PhD Biomedical Engineering)

**Chief Complaint:** "I'm having severe joint pain in my right shoulder and my skin feels tingly — it started 30 minutes into the EVA."

**History of Present Illness:**
Dr. S.K. was performing an extravehicular activity (EVA) during a space station maintenance mission when she developed progressive right shoulder pain described as deep, boring, and aching. The pain began approximately 30 minutes into the EVA despite completing the standard pre-breathe protocol (2 hours of 100% O2 at cabin pressure followed by suit pressurization at 4.3 psi). She initially attributed the pain to suit ergonomics but it intensified and was accompanied by cutaneous mottling and paresthesias over the right upper extremity.

The EVA was terminated early and the astronaut returned to the airlock. Upon repressurization to cabin pressure (14.7 psi), symptoms partially improved but did not resolve. She subsequently developed mild cognitive difficulty with word-finding problems noted by crew members. No chest pain, dyspnea, or visual changes were reported.

Review of the pre-breathe protocol revealed that Dr. S.K. had performed moderate exercise (resistance training) approximately 4 hours before the EVA, which may have increased tissue nitrogen loading. Additionally, she had been on the station for only 3 weeks, arriving from Earth where higher ambient pressure exposure may have contributed to residual nitrogen stores.

**Past Medical History:**
- One prior episode of mild Type I DCS (skin bends only) during altitude chamber training, resolved with descent — 8 years ago
- Patent foramen ovale (PFO) screening: bubble study equivocal (trace shunt detected under Valsalva)
- Otherwise medically qualified for spaceflight

**Medications:**
- Multivitamin
- Melatonin 3 mg PRN for circadian adjustment

**Social History:**
- Non-smoker, no alcohol use during mission
- Recreational SCUBA diver (certified, 40+ dives, no DCS history with diving)
- Third spaceflight; two prior EVAs without incident

**Family History:**
- Non-contributory

### Physical Examination
- **Vital Signs:** BP 124/78 mmHg, HR 92 bpm, RR 16, SpO2 98% on cabin air, Temp 36.9°C
- **General:** Alert but mildly anxious, intermittent word-finding pauses noted
- **Skin:** Cutis marmorata (mottled, marbled appearance) over right shoulder and proximal upper arm; mild subcutaneous crepitus palpated over right deltoid region
- **Musculoskeletal:** Tenderness to palpation over right glenohumeral joint; pain worsened with movement; no effusion
- **Neurological:** Oriented to person, place, time; word-finding difficulty on formal testing; cranial nerves intact; motor strength 5/5 bilateral upper and lower extremities; sensation intact to light touch and pinprick; proprioception normal
- **Cardiovascular:** Tachycardic, regular rhythm, no murmurs
- **Pulmonary:** Clear to auscultation bilaterally

### Workup and Results

**Laboratory Studies:**
| Test | Result | Reference Range |
|------|--------|-----------------|
| Hemoglobin | 12.8 g/dL | 12.0-15.5 g/dL |
| Hematocrit | 38% | 35.5-44.9% |
| Platelet count | 198 x 10⁹/L | 150-400 x 10⁹/L |
| D-dimer | 0.82 mg/L FEU | <0.50 mg/L FEU |
| CRP | 3.2 mg/L | <3.0 mg/L |
| CPK | 145 U/L | 26-192 U/L |
| ABG (cabin air) | pH 7.43, pCO2 38, pO2 92 | pH 7.35-7.45 |

**Imaging/Additional Studies:**
- **Portable ultrasound (ISS):** No pneumothorax; no joint effusion in right shoulder; echogenic foci noted in right subclavian vein (venous gas emboli)
- **Transcranial Doppler (TCD):** Multiple high-intensity transient signals (HITS) detected bilaterally, consistent with cerebral microemboli
- **Neurocognitive testing (ISS protocol):** Mild impairment in verbal fluency and working memory compared to pre-flight baseline

### Clinical Image

![Pathophysiology of decompression sickness in space](case_02_image.jpg)

*Illustration showing nitrogen bubble formation in tissues and vasculature during EVA decompression from 14.7 psi cabin pressure to 4.3 psi suit pressure in microgravity. Source: Educational illustration.*

### Diagnosis
**Decompression Sickness, Type II (Neurological Involvement) with Type I Features (Musculoskeletal and Cutaneous)**

**Key Diagnostic Criteria:**
- Symptom onset during EVA with decompression from 14.7 psi to 4.3 psi
- Musculoskeletal pain (the "bends") in right shoulder
- Cutaneous manifestations (cutis marmorata) indicating skin involvement
- Neurological symptoms (word-finding difficulty) elevating to Type II classification
- Venous gas emboli confirmed on ultrasound with cerebral microemboli on TCD
- Possible right-to-left shunt via PFO as mechanism for arterial gas embolism and neurological involvement

### Treatment Plan
1. Immediate 100% oxygen via mask (continuous until symptoms resolve)
2. IV fluid resuscitation with normal saline (1.5 L bolus, then 125 mL/hr) to reduce hemoconcentration and improve microcirculation
3. Oral aspirin 325 mg (if no contraindications) for antiplatelet effect
4. ISS hyperbaric treatment protocol: repressurization of affected module if capability exists; consultation with ground-based hyperbaric medicine specialists
5. Serial neurocognitive assessments every 6 hours
6. If symptoms persist or worsen: emergency medical evacuation via Soyuz/Crew Dragon for ground-based hyperbaric oxygen therapy (USN Treatment Table 6)
7. Formal PFO evaluation with transesophageal echocardiography upon return to Earth
8. Restriction from future EVA activities pending aeromedical board review

### Key Learning Points
- Decompression sickness in spaceflight occurs due to the pressure differential between cabin atmosphere (14.7 psi) and EVA suit pressure (4.3 psi), a ratio of 3.4:1 that exceeds safe decompression limits without pre-breathe
- The standard pre-breathe protocol (100% O2 for 2-4 hours) reduces but does not eliminate DCS risk; exercise before EVA can paradoxically increase tissue nitrogen loading
- Type II DCS involves the central nervous system and requires more aggressive treatment; the presence of a PFO creates a pathway for venous gas emboli to reach the arterial circulation (paradoxical embolism)
- In-flight treatment of DCS on the ISS is limited; definitive hyperbaric oxygen therapy requires return to Earth, making prevention paramount
- Prior history of DCS, even mild, is a risk factor for recurrence and should prompt thorough PFO screening

---

## Case 3: Circadian Disruption in Commercial Airline Crew

### Patient Presentation
**Demographics:** 51-year-old female senior commercial airline captain (Boeing 787, international long-haul routes)

**Chief Complaint:** "I can't sleep properly anymore, I'm exhausted all the time, and I nearly missed a critical callout on approach last week."

**History of Present Illness:**
Captain L.H. presents to the aviation medical examiner for her annual Class 1 medical certificate renewal. Over the past 8 months, she has been experiencing progressively worsening insomnia, excessive daytime somnolence, and cognitive difficulties she attributes to her international route schedule. She typically flies transmeridian routes crossing 8-12 time zones (North America to Asia-Pacific) with layovers of 24-36 hours before return flights.

She reports difficulty initiating sleep at layover destinations (sleep onset latency of 90-120 minutes), frequent nocturnal awakenings, and non-restorative sleep averaging 3-4 hours per sleep period. She has been using over-the-counter diphenhydramine (50 mg) nightly during layovers, which provides sedation but leaves her feeling cognitively impaired the following morning. She has also increased her caffeine intake to 6-8 cups of coffee per day.

Her husband reports that she has become increasingly irritable, has gained approximately 8 kg over the past year, and occasionally appears disoriented upon awakening at home. She endorses depressed mood, decreased libido, and two episodes of near-microsleep during cruise phase of flight in the past month, the second of which resulted in delayed response to an ATC callout that was caught by her first officer.

**Past Medical History:**
- Mild gastroesophageal reflux disease (GERD)
- Pre-diabetes (HbA1c 5.9% on last check, 14 months ago)
- No prior psychiatric history

**Medications:**
- Omeprazole 20 mg daily
- Diphenhydramine 50 mg PRN (nightly during layovers)
- Melatonin 5 mg PRN (inconsistent use, reports variable efficacy)

**Social History:**
- Non-smoker; social alcohol (2-3 glasses wine per week, never within 8 hours of duty)
- 28 years of commercial aviation experience, 14 years as captain
- Married, two adult children
- Minimal regular exercise due to fatigue and schedule constraints
- Average monthly flight hours: 85-90 (near regulatory maximum)

**Family History:**
- Mother: type 2 diabetes, breast cancer (age 62)
- Father: hypertension, coronary artery disease (CABG age 64)

### Physical Examination
- **Vital Signs:** BP 142/88 mmHg, HR 82 bpm, RR 14, SpO2 97% on room air, Temp 36.7°C, BMI 29.4 kg/m²
- **General:** Appears fatigued with periorbital darkening; oriented but mildly psychomotor slowed
- **HEENT:** Mallampati Class III airway; no thyromegaly
- **Cardiovascular:** Regular rate and rhythm, no murmurs; bilateral lower extremity trace edema
- **Abdomen:** Soft, non-tender, central adiposity
- **Neurological:** Alert and oriented x4; cranial nerves intact; mild difficulty with serial 7s and digit span (backward) compared to prior assessments
- **Psychiatric:** PHQ-9 score: 12 (moderate depression); Epworth Sleepiness Scale: 16 (severe excessive daytime sleepiness); GAD-7: 8 (mild anxiety)

### Workup and Results

**Laboratory Studies:**
| Test | Result | Reference Range |
|------|--------|-----------------|
| HbA1c | 6.3% | <5.7% (normal) |
| Fasting glucose | 118 mg/dL | 70-100 mg/dL |
| TSH | 5.8 mIU/L | 0.4-4.0 mIU/L |
| Free T4 | 0.9 ng/dL | 0.8-1.8 ng/dL |
| Cortisol (0800) | 24.2 μg/dL | 6.2-19.4 μg/dL |
| Melatonin (salivary, 2300 local) | 8.2 pg/mL | 10-50 pg/mL |
| Vitamin D (25-OH) | 18 ng/mL | 30-100 ng/mL |
| Total cholesterol | 228 mg/dL | <200 mg/dL |
| LDL | 148 mg/dL | <100 mg/dL |
| Triglycerides | 186 mg/dL | <150 mg/dL |
| ALT | 42 U/L | 7-56 U/L |

**Imaging/Additional Studies:**
- **Polysomnography:** Sleep efficiency 62%, prolonged sleep onset latency (45 min), reduced REM sleep (12% of total sleep time), no obstructive sleep apnea (AHI 3.2/hr)
- **Actigraphy (14-day):** Severely fragmented sleep-wake pattern with no consistent circadian rhythm; average total sleep time 4.8 hours/24-hour period
- **Psychomotor Vigilance Task (PVT):** Mean reaction time 342 ms (impaired; baseline 241 ms); 8 lapses per 10-minute test (significant impairment)
- **Continuous glucose monitoring (7-day):** Postprandial spikes to 195 mg/dL, time in range (70-140) only 58%

### Clinical Image

![Circadian rhythm disruption in transmeridian aircrew](case_03_image.jpg)

*Diagram showing the disruption of the circadian melatonin-cortisol axis in transmeridian flight crew, with comparison of normal vs. disrupted sleep-wake cycles and metabolic consequences. Source: Educational illustration.*

### Diagnosis
**Circadian Rhythm Sleep-Wake Disorder, Shift Work/Jet Lag Type (Chronic) with Secondary Metabolic Syndrome and Subclinical Hypothyroidism**

**Key Diagnostic Criteria:**
- Chronic insomnia and excessive sleepiness temporally associated with recurring transmeridian flight schedule
- Objective evidence of circadian disruption: suppressed evening melatonin, elevated morning cortisol, fragmented actigraphy pattern
- Functional impairment: cognitive deficits on PVT, near-microsleep episodes during flight operations
- Metabolic consequences: progression from pre-diabetes to diabetes (HbA1c 6.3%), dyslipidemia, weight gain, elevated TSH
- Duration exceeding 3 months with significant occupational and personal impairment

### Treatment Plan
1. **Immediate aeromedical action:** Temporary removal from international long-haul routes; reassignment to domestic short-haul schedule pending stabilization
2. **Sleep hygiene and circadian realignment:**
   - Strategic timed light exposure (10,000 lux light box, 30 min at destination morning)
   - Timed melatonin: 0.5 mg (low-dose) taken 5 hours before desired bedtime at destination
   - Discontinue diphenhydramine (anticholinergic burden, cognitive impairment, not FAA-approved)
3. **Pharmacological (aviation-compatible):**
   - Melatonin 0.5 mg as above (acceptable to most civil aviation authorities with restrictions)
   - Consider ramelteon 8 mg if melatonin insufficient (requires FAA HIMS review)
4. **Metabolic management:**
   - Endocrinology referral for new diabetes diagnosis and subclinical hypothyroidism
   - Metformin 500 mg BID with titration
   - Vitamin D3 2,000 IU daily
   - Dietary counseling focused on glycemic control and anti-inflammatory nutrition
   - Structured exercise program: 150 min/week moderate aerobic activity
5. **Mental health support:**
   - Cognitive behavioral therapy for insomnia (CBT-I), 6-session program
   - Psychiatry evaluation for moderate depression (PHQ-9: 12); may require SSRI with FAA reporting
6. **Follow-up:** Repeat PVT, actigraphy, and metabolic labs at 3 months; Class 1 medical certificate decision pending treatment response

### Key Learning Points
- Chronic circadian disruption in aviation personnel is an occupational hazard with cumulative health consequences including metabolic syndrome, cardiovascular disease, depression, and cancer (IARC classifies shift work involving circadian disruption as Group 2A — probably carcinogenic)
- The suprachiasmatic nucleus can only adjust by approximately 1-1.5 hours per day, making rapid transmeridian travel inherently disruptive; eastward travel is typically more difficult than westward
- Diphenhydramine and other first-generation antihistamines, while sedating, impair cognitive function for 12+ hours and are incompatible with aviation duty; they do not promote restorative sleep architecture
- Low-dose melatonin (0.3-0.5 mg) is more effective as a chronobiotic than high-dose (5-10 mg) formulations, which cause supraphysiologic levels and can worsen circadian disruption
- Aeromedical decision-making must balance the pilot's health, career, and public safety; fatigue-related performance decrements pose unacceptable risk to flight safety and require prompt intervention